Why the letters matter
PEX is grouped by how the plastic is cross-linked during manufacturing, labeled A, B and C. The differences affect how flexible the tubing is and which fittings it works with. For a homeowner, the practical question is less which letter is best and more whether the contractor is using a tubing and fitting system that are made to work together.
Mixing brands or fitting styles without checking compatibility is one of the things a careful installer avoids. Ask what the plan is and get it in writing.
Terms you will hear
- PEX-A
- Tubing cross-linked by the peroxide method. Generally the most flexible type and often used with expansion fittings.
- PEX-B
- Tubing cross-linked by the silane method. Somewhat stiffer and commonly joined with crimp or clamp rings.
- PEX-C
- Tubing cross-linked by electron beam. Less common in whole-house repipes.
- Expansion fitting
- The tubing end is expanded, slipped over a fitting, and shrinks back to seal, sometimes with a ring.
- Crimp or clamp ring
- A metal ring compressed around tubing and fitting with a dedicated tool.
- Manifold
- A central block that feeds separate lines to each fixture, often with individual shutoffs.
- Home run
- A layout where each fixture has its own line back to the manifold.
Manifold versus trunk-and-branch
Manifold layout
- Each fixture fed by its own line.
- Individual shutoffs in one place.
- More tubing overall, fewer hidden joints.
Trunk and branch
- Main lines with branches to each room.
- Similar to how copper is usually laid out.
- Less tubing, more fittings along the way.
Installation details worth checking
- Tubing kept out of direct sunlight, including in garages with windows.
- Adequate clearance from heat sources such as flues and recessed lights.
- Proper supports so lines do not sag or rub.
- Protection plates where tubing passes through studs near the surface.
- Transition fittings where PEX meets the water heater or metal pipe.
Questions to ask
- Which PEX type and fitting system will you use, and why?
- Will there be a manifold, and where will it be accessible?
- How will the attic runs be supported and protected?
- What will connect the PEX to the water heater?
Common questions
Is PEX-A better than PEX-B?
Each has its uses. What matters most is that the tubing and fittings are a matched system installed correctly. Ask your plumber to explain their choice.
Can rodents damage PEX?
Plastic tubing in attics can be chewed. Ask how the installer protects lines and whether any pest issues should be dealt with first.
Can PEX be used outside?
PEX should not be left exposed to sunlight. Hose bibs and exterior runs are often done in copper or protected appropriately.
General information for Yorba Linda, not a quote or professional advice. In an emergency, call 911.